This invention relates to an apparatus for acquiring in vivo medical images in real time at video rates utilizing optical, ultrasonic or opto-acoustical sensors.
Various noninvasive medical imaging techniques have been developed for acquiring images of internal body organs for diagnostic purposes. These techniques generally involve introducing a catheter into the body and advancing it to the site of interest. Typically, a catheter equipped at its remote end with an imaging unit appropriate for the desired images would be inserted into the biopsy channel of a standard endoscopic device. Images are collected at the imaging unit and transmitted via optical fibre to image processing and analysis equipment external to the body.
Imaging techniques that utilize ultrasound, optical coherence tomography (OCT) or optical coherence microscopy (OCM) can reveal sub-surface biological structure providing benefits in the diagnosis of early cancer tumors and precise guidance for excisional biopsy.
Optical coherence tomography (OCT) is particularly desirable for in vivo imaging since it can provide tomographic images of sub-surface biological structure with approximately 4-10 xcexcm resolution. It is analogous to ultrasound imaging in that two-dimensional images of structure are built up from sequential adjacent longitudinal scans of backscatter versus depth into the tissue. However, in OCT, the probing radiation is infrared light rather than sound waves, thus higher resolution measurements are possible. The usefulness of OCT has been well demonstrated in vitro on tissue samples and in vivo on easily accessed external organs such as the skin, teeth and eye. In addition, OCT has great potential for lung cancer detection, particularly for lesions located in the periphery airways where they cannot be reached by conventional endoscopes or catheters.
At present, in vivo imaging tends to be limited to larger organs that can readily accept a catheter. While small diameter catheters that could access smaller organs such as the peripheral airways of the lungs have been developed, size constraints continue to limit the functionality of the scanning heads of these catheters. In particular, small diameter catheters that include scanning units able to collected images at video rates are not yet available for access into organs such as the lung that has a complex branching system.
Conventional fibre-optic OCT systems employ a single rotating scan unit with image sensors at the distal end of the catheter which produce a radar-like scan of the site of interest. The scan unit is driven by a rotating wire or flexible drive-cable coupled to a motor at the end of the catheter external to the body. The configuration of the rotating drive element which extends the length of the catheter lumen creates a number of problems. Torsional flexing of the rotating drive element make it difficult to precisely control the position and speed of rotation of the scanning unit. In addition, friction and wear in the lumen of the catheter caused by this rotating element also adversely affect the operation and reliability of the apparatus. Rotational and frictional problems may be further exacerbated when the catheter is subjected to a tight bending radius.
In order to be appealing for in situ diagnostics, it must be possible to obtain near real-time imaging at video rates. Conventional catheters employing fibre-optic OCT technology use a single fibre and a single path interferometer to perform optical coherence tomography. Therefore, the frame rate is limited by the scanning rate of the reference arm of the interferometer. Furthermore, if contemplated, existing designs would be compelled to place additional elements in a coaxial configuration.
One of the best OCT systems developed to date utilizes a Fourier-domain rapid scanning optical delay line with a resonant scanner and performs 4000 A-scans per second (Rollins 1998) To run the system at video rates, only 125 A-scans per frame can be achieved, thus degrading the resolution of the images obtained. To obtain a high-resolution image of 500 A-scans per frame, only 8 frames per second of imaging can be performed. Faster scanning systems are being designed, but are not yet available.
Similar problems exist in endoscopic ultrasound where rotational scanning is used.
In view of the foregoing problems with existing catheter designs, it is apparent that there is a need for a new design that relies on an alternative scheme to drive the scanning unit and that permits imaging of internal organs in real time at video rates. It is also necessary for the catheter to be of sufficiently small diameter and sufficient flexibility to access small diameter regions of internal organs such as the lungs, coronary arteries, fallopian tubes or biliary ducts.
A novel apparatus for in vivo imaging has been developed that addresses the problems discussed above. Accordingly, the present invention provides apparatus for acquiring in vivo images of a site of interest within the internal organs of a body comprising:
an elongate, flexible catheter having a longitudinal axis and lumen defined by lumen walls, the catheter being introducible into the body and having a first end that remains external to the body and a second end positionable adjacent the site of interest;
a movable scanning unit having at least one sensor for acquiring images housed adjacent to the second end of the catheter;
communication means extending through the lumen of the catheter from the at least one sensor to communicate the sensor with the first end of the catheter;
a drive mechanism to control movement of the movable scanning unit from first external end of the catheter to acquire multiple images of the site of interest, the drive mechanism having a control element extending the length of the catheter lumen and adapted for linear movement within the lumen.
In a preferred embodiment, the apparatus of the present invention relies on a drive mechanism incorporating an actuating rod or wire that moves linearly within the lumen of the catheter to control movement of the scanning unit. The resulting movement of the scanning unit can be linear or rotational. This arrangement is not prone to the friction and wear problems of prior designs. Furthermore, the drive mechanism is flexible enough to operate without binding despite the tight radius of curvature that a catheter may experience when inserted into small diameter regions of internal organs such as the upper lobes of the lung.
The drive mechanism is extremely compact which permits the drive mechanism to be incorporated into extremely small diameter catheters for insertion into organs with small diameter passages. The drive mechanism is also relatively simple with few moving parts so that consistent, reliable operation is assured.
In addition, the apparatus of the present invention contemplates the use of a scanning unit having multiple sensors to increase the image acquisition rate. For OCT scanning, the image acquisition rate can be increased to over 30 frames per second while maintaining the high resolution of 500 A-scans per frame. An A-scan is the longitudinal or depth scan of the tissue being examined. This scan is generated by modulating the path length of the reference arm of the optical system, which produces a delay in the return of the reference signal. The use of a linearly movable control rod or wire to actuate the scan head removes the constraint of having coaxial optical fiber(s) as required by a rotating design. This permits additional fibre-optics to be incorporated in the lumen or lumens of the catheter.